In this study, we wish to identify and characterise the alternative pathway through which environmental estrogens may mediate their intracellular effects. Three human breast cancer cells were employed including MCF-7 cells, which express both ERα and ERβ; MDA-MB-231 cells, which express ERβ but not ERα; and SKBR-3 cells, which express neither ERα nor ERβ. The effect of environmental estrogenic compounds on intracellular calcium ion concentration ([Ca²⁺]_i, was measured by fura-2 fluorescence and compared to that of 17β-estradiol (E2). A rapid and maintained increase in [Ca²⁺]_i was observed following the application of nanomolar concentrations (0.1-100 nM) of E2 and the environmental estrogens bisphenol-A, o.p’-DDT, diethylstilbestrol and 4-tert-octylphenol regardless of ERα and ERβ expression. The steroid-induced [Ca²⁺]_i response was completely abolished by incubating the cells in Ca²⁺-free medium, suggesting that the source of Ca²⁺ increase is extracellular. Pre-treating the cells with the ER antagonist ICI 182,780 had no effect on either basal nor the steroid-triggered [Ca²⁺]_i response. In summary, we have demonstrated ER independent acute non-genomic effects of environmental estrogenic compounds at nanomolar concentrations on [Ca²⁺]_i. The results of this study demonstrate an alternative to the classical genomic pathway to explain the potent effects of these endocrine disruptors.